JP2002234966A - Rubber composition for tire tread - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve initial and after-aging fatigue properties under a constant strain without lowering heat-aging resistance and elongation at break. SOLUTION: The rubber composition for a tire tread comprises on the basis of 100 pts.wt. at least one kind of vulcanizable rubber, a sulfur compound (1) to be represented by the formula: -(SxR1)n- (wherein R1 is an organic group; x is a number of 3-5 on the average; and n is an integer of 1-100) and sulfur (2) at a weight ratio of sulfur compound (1) to sulfur (2) of >=0.5 and, simultaneously, >=0.5 pts.wt. sulfenamide vulcanization accelerator (3), and furthermore so as to render the compounding amount of sulfur compound (1), sulfur (2), and sulfenamide vulcanization accelerator (3) at a weight ratio of [(1)+(2)]/(3)>2.2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition for a tire tread, and more particularly to a rubber composition for at least one kind of vulcanizable rubber, which is compounded with a reinforcing filler, a specific sulfur compound and the like to obtain a heat aging resistance. The present invention relates to a rubber composition for a tire tread capable of improving fatigue resistance while maintaining high elongation at break.

[0002]

2. Description of the Related Art Heavy-duty tires such as tires for trailer vehicles used for long-distance transportation are required to have a longer life. In order to respond to such a demand, it is well known that a groove in a tread portion is deepened as a method of extending the life of a tire. However, there is a problem that a groove bottom crack easily occurs due to fatigue. On the other hand, the fatigue resistance of a vulcanizable rubber composition is better as the number of polysulfide cross-links increases, but as the number of polysulfide cross-links increases, the heat aging resistance deteriorates, and the fatigue resistance after aging is greatly reduced. There is. Further, when the crosslinking density of the rubber is increased, the decrease in fatigue resistance due to aging is small, but there is a problem that the level of fatigue resistance in the initial stage of the rubber composition before aging is reduced.

[0003]

SUMMARY OF THE INVENTION The present inventors maintain a heat aging resistance / high elongation at break by using a specific polysulfide compound / sulfur / sulfenamide vulcanization accelerator in a specific ratio. While improving fatigue resistance. In particular, the composition of the present invention is suitable as a rubber composition for a heavy-load tire tread that requires a deep groove and high fatigue resistance (groove crack resistance, etc.). Further, when the polybutanediene rubber is combined with the rubber composition and blended, the fatigue resistance can be further improved.

[0004] That is, an object of the present invention is to provide a rubber composition for a tire tread in which the initial strain and the constant strain fatigue after aging are improved while maintaining heat aging resistance / high elongation at break.

[0005]

According to the present invention, at least one vulcanizable rubber (100 parts by weight) has the formula (I):-(S _x R ¹ ) _n- (I) , R ¹ represents an organic group, x is an average of 3 to 5, n is 1
Of sulfur compound (1) and sulfur (2) represented by the following formula (1) / (2) is 0.5 or more and a sulfenamide-based compound: The vulcanization accelerator (3) is 0.5 parts by weight or more, and the compounding amounts of the sulfur compound (1), the sulfur (2) and the sulfenamide vulcanization accelerator (3) are in a weight ratio [( 1) +
(2)] / (3)> A rubber composition for a tire tread is provided which is compounded so as to satisfy 2.2.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have conducted studies to solve the above-mentioned object, and as a result, using a sulfur compound (1) having a specific structure, a sulfur compound (2) and a sulfenamide-based compound. By controlling the sulfur cross-linking structure of the rubber by blending the accelerator (3) in a specific ratio, the rubber composition having improved initial and aging constant strain fatigue without lowering heat aging resistance and elongation at break. I succeeded in getting things.

As described above, the rubber composition for a tire tread according to the present invention comprises a vulcanizable rubber and the sulfur compound (1) and the sulfur (2) of the formula (I) at a certain ratio. And a specific amount of a sulfenamide vulcanization accelerator (3). The organic group R ¹ of the sulfur compound of the formula (I) is preferably an oxyalkylene group having 2 to 10 carbon atoms and / or a polyoxyalkylene group having 2 to 10 carbon atoms and 2 to 10 oxygen atoms. Can be

The sulfur compound of the formula (I) used in the present invention includes a Mooney viscosity of a raw material (JIS K).
According to 6300, using an L-shaped rotor, measured at 100 ° C., a preheating time of 1 minute, and a rotor rotation time of 4 minutes) are 100
Or less, preferably 85 or less, and a number average molecular weight of 2
A polysulfide polymer of from 00 to 15000, preferably from 1000 to 12000, of the formula (II):

R ³ S _z R ² (S _y R ² ) _m S _z R ³ (II)

(Wherein R ² is an oxyalkylene group having 2 to 10 carbon atoms and / or 2 to 10 carbon atoms and 2 to 2 oxygen atoms)
10 is a polyoxyalkylene group, R ³ is at least one functional group selected from hydrocarbon groups having 1 to 30 carbon atoms, preferably 3 to 20 carbon atoms (for example, allyl group, benzyl group, etc.); y is a number of 1-6, preferably 2-3, z is a number of 1-6, preferably 2-3, and m is an integer of 1-50, preferably 5-40) Is a polysulfide polymer in which y is an average of 3 to 5, z is an average of 3 to 5, and R ^{2 in the} formula (II) is preferably a compound represented by the following formula: And polysulfide polymers represented by (III).

—C ₂ H ₄ OC _{m ′} H _{2m ′} OC ₂ H ₄ − (III)

(In the formula, m ′ is an integer of 1 or 2.)

As the vulcanizing agent of the present invention, sulfur (2) (or another sulfur donor) is used in addition to the sulfur compound (1). Such sulfur (2) can be any sulfur commonly used for vulcanization of rubber, including sublimated sulfur, precipitated sulfur, sulfur, colloidal sulfur, and the like.

In the vulcanized rubber composition according to the present invention,
The sulfur compound (1) of the formula (I) and the sulfur (2) are added at a ratio of (1) / (2) of not less than 0.5, preferably not less than 1.0 to 100 parts by weight of the vulcanizable rubber. (1) + at 5.0
The total amount of (2) is 8 parts by weight or less, preferably 1 to 5 parts by weight, more preferably 2 to 4 parts by weight. This (1)
If the ratio of / (2) is less than 0.5, a desired crosslinked structure cannot be obtained, and if the total amount of the sulfur compound (1) + sulfur (2) exceeds 8 parts by weight, scorch properties in unvulcanized physical properties, etc. Is not preferable because it deteriorates.

The rubber composition according to the present invention may contain, as a reinforcing filler, carbon black, silica, clay, talc, surface-treated carbon black or the like which has been generally compounded for rubbers. Can be.
The compounding amount of the reinforcing filler is preferably a vulcanizable rubber 1
It is 40 to 75 parts by weight with respect to 00 parts by weight.

In the vulcanized rubber composition according to the present invention,
The sulfenamide vulcanization accelerator (3) is used in an amount of 0.5 parts by weight or more, preferably 0.6 to 2.5 parts by weight, more preferably 0.8 to 0.5 parts by weight, based on 100 parts by weight of the vulcanizable rubber. 1.8
Parts by weight, and the weight ratio [(1) + (2)] /
(3) is more than 2.2, preferably 2.4 or more, and more preferably 2.5 to 4.0. The addition of such a vulcanization accelerator is preferable because a desired crosslinked structure can be obtained and elongation at break, heat aging resistance and fatigue resistance can be improved. [(1) + (2)]
When the value of / (3) is not more than 2.2, fatigue resistance and elongation at break tend to decrease, which is not preferable.

Examples of the sulfenamide vulcanization accelerator that can be used in the present invention include N-cyclohexyl-2-benzothiazole sulfenamide (C
BS), Nt-butyl-2-benzothiazolesulfenamide (TBBS), N-oxyethylene-2-benzothiazolesulfenamide (OBS), N, N '
-Diisopropyl-2-benzothiazolesulfenamide (DPBS) and the like.

As the vulcanizable rubber used in the present invention, for example, any vulcanizable rubber conventionally compounded generally for tires and other rubber applications, specifically, natural rubber (NR ), Butadiene rubber (BR), isoprene rubber (IR), chloroprene rubber (CR), butyl rubber (IIR), various styrene-butadiene rubbers (S
Diene rubbers such as BR) and mixtures thereof. In addition, natural rubber alone or natural rubber 90
The use of a blend of 100 to 50 parts by weight of polybutadiene rubber and 10 to 50 parts by weight of polybutadiene (total amount of 100 parts by weight) is
It is preferable from the point of elongation at break.

In the rubber composition for a tire tread according to the present invention, 0.05 to 1 part by weight of a scorch inhibitor such as N- (cyclohexylthio) phthalimide is added to 100 parts by weight of a vulcanizable rubber. It is preferable because it has excellent scorch properties (rubber scorch properties) and improves workability.

The rubber composition according to the present invention contains, in addition to the above components, other fillers conventionally used as rubber compounding components, activators such as zinc oxide and magnesium oxide, and the like. Waxes, antioxidants, antiozonants, mastication accelerators, adhesive resins, process oils, vulcanization retarders, etc. can be added, and the compounding amounts are in a general range unless the purpose of the present invention is impaired. It can be.

[0021]

EXAMPLES Hereinafter, the present invention will be further described with reference to Examples, but it goes without saying that the scope of the present invention is not limited to these Examples. Standard Examples 1-4, Comparative Examples 1-12 and Examples 1-9 Each component of the composition (parts by weight) shown in Tables I and II was prepared according to a conventional method, that is, excluding the sulfur compound, sulfur and the vulcanization accelerator. Each component was kneaded for 3 to 5 minutes in a 1.8 liter closed mixer (Banbury mixer), and the internal temperature was 165 ° C.
The contents were released when the temperature reached ± 5 ° C. Next, the remaining components were blended and mixed with an 8-inch open roll to obtain a rubber composition.

Next, the rubber composition obtained above was subjected to 15 × 15 ×
Press vulcanization was performed in a 0.2 cm mold at 150 ° C. for 30 minutes to prepare a target test piece, and vulcanization properties were evaluated. The results are shown in Tables I and II. In addition, the test method of a vulcanization property is as follows. 1) Elongation at break (%): Initial and after aging (90 ° C x 48)
Time) value according to JIS K6301 (dumbbell-shaped No. 3 type)
2) JIS hardness: Measured at 20 ° C. according to JIS K6253. 3) Constant strain fatigue: A JIS No. 3 dumbbell test piece was fixed with a chuck, and 70% strain was 40 minutes per minute at room temperature.
The test was repeated 0 times, and the number of times when the test piece was cut was measured.

Tables I and II Footnotes Sulfur compounds (tetrasulfide): polysulfide polymer (Toray Reticol, LP-32) in the presence of an equivalent amount of triethylamine, adding an excess of allyl chloride.
After the reaction and the filtration of the amine hydrochloride, excess allyl chloride was distilled off. Powder sulfur 3
6.2 g and 0.5 g of triethylamine were added, and 90 ° C.
For 1 hour to obtain a viscous polysulfide (number-average molecular weight: about 5,500). Powdered sulfur: 5% oil-extended sulfur Vulcanization accelerator CBC: N-cyclohexyl-2-benzothiazole sulfenamide Vulcanization accelerator TBBS: Nt-butyl-2-benzothiazole sulfenamide

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

As is evident from the results shown in the table, by blending a sulfur compound / sulfur / sulfenamide vulcanization accelerator having a specific structure with a specific ratio in a vulcanizable rubber according to the present invention. In addition, constant strain fatigue resistance can be improved while maintaining heat aging resistance / high elongation at break.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // (C08L 21/00 (C08L 21/00 81:04) 81:04) (72) Inventor Fumi Yayanagi No.2-1 Oiwake, Hiratsuka-shi, Kanagawa F-term in Yokohama Rubber Co., Ltd. Hiratsuka Works 4J002 AC001 AC011 AC021 AC031 AC061 AC081 AC091 CN022 DA046 EV277 FD010 FD030 FD142 FD146 FD157 GN01

Claims (4)

[Claims] 1. At least one vulcanizable rubber 100
Formula (I) _:-( S _x R ¹ ) _n- (I) wherein R ¹ represents an organic group, x is a number of 3 to 5, and n is 1 to 1 part by weight. The sulfur compound (1) and the sulfur (2) represented by the following formula:
(2) is at least 0.5 and the sulfenamide-based vulcanization accelerator (3) is at least 0.5 part by weight, and the sulfur compound (1), sulfur (2) and sulfenamide-based The amount of the vulcanization accelerator (3) is the weight ratio [(1) + (2)]
/ (3) A rubber composition for a tire tread, which is blended so as to satisfy 2.2. 2. The rubber composition according to claim 1, wherein the vulcanizable rubber is a natural rubber. 3. The rubber composition according to claim 2, wherein the vulcanizable rubber contains 10 to 50% by weight of a polybutadiene rubber based on the total amount of the rubber. 4. The rubber composition according to claim 1, which has a hardness of 65 or more.